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I made a mistake
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Looks like it. Nothing eles but the diode I installed in that spot On Oct 23, 2017 9:18 PM, "Vince Vielhaber" <vev@...> wrote:
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Vince Vielhaber
You might want to tombstone it to make sure that is what's smoking.
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Vince. On 10/23/2017 10:32 PM, Barrett O wrote:
Looks like it. Nothing eles but the diode I installed in that spot --
Michigan VHF Corp. |
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tombstone?? On Oct 23, 2017 10:00 PM, "Vince Vielhaber" <vev@...> wrote: You might want to tombstone it to make sure that is what's smoking. |
¿ªÔÆÌåÓýMy gut instinct is that that diode is installed incorrectly
somehow.? Double check to make sure you are not shorting the power
supply with the diode.? I would also highly recommend you add a 1
amp fuse to your power input while you are sorting this out. On 10/23/2017 10:32 PM, Barrett O wrote:
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If you reversed the power leads into the main bitx40 board, I suspect surprisingly little would blow.
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D7 and C130 are meant to be a snubber across the coil of K1, but got wired up wrong. They are not across the coil (pins 7 and 8 of the relay) but instead are from +12v to ground. They should have been wired up like D8 and C164 at K2, directly across the relay coil. Since D7 and C130 ?aren't wired up right, they aren't serving any purpose and can be removed from the board. U2 is probably blown, as the LM78L09 is not built to deal with a negative voltage at the input. But damage probably stopped there, as Q8 and Q9 have no path from +12 to gnd of less than 1kohm. Check for 9v at U2 pin 1, if you don't see 9v then replace U2. Or if you are brave, just wire across U2 from pin 3 to pin 1 and cut pin 2 loose from ground, you don't really need a regulator there if not using the analog vfo.? Q7 has mostly that 470 ohm emitter resistor to stop excessive reverse current, but probably survived. I'm not really sure how Q7 (or any of the other transistor amps) would behave in the face of a reverse supply. U1 and Q16 have a handy reverse power protection diode at D18, so should have no trouble. Likewise with the three BiDi RF amps, they all have a diode in series with the 12v supply. There is no path around Q12 that sees less than 1kohm, and 12ma shouldn't fry anything there. Likewise with Q10 and Q11. If you did not press the PTT button, then the stuff around Q13, Q14 and U3 never saw power, and should be fine. ? If you wired up PA-PWR1 with a reversed 12v supply and powered that up, it could have blown the IRF510 as it has a reverse diode from drain to source. ?But more likely the coil at L8 or T7 would burn first. If you did not wire up PA-PWR1 in reverse, then that stuff should all be fine. The Raduino on the other hand is probably toast if it saw reversed supplies. ? Maybe you do want to get U2 working again, supplying 9v to the analog vfo so you can install a coil at L4 and play with the rig till a new Raduino arrives. That's just a quick survey, I probably got some stuff wrong. Could well be something more than U2 that blew on the main board. And perhaps somebody can figure out how to bring your Raduino back from the dead. May not be trivial to figure all of this out without a scope and some idea of what's going on. At worst, consider this a nice cheap $59 lesson in what not to do, ?and go order another unit from hfsigs. ? Jerry, KE7ER On Mon, Oct 23, 2017 at 07:00 pm, Barrett O wrote: Well I got around to install a diode still no luck. I had some 1N914 which are supposed to be electrically the same. I ended up accidentally ripping one of the traces off that seems to lead to the relay. I drilled and installed diode. I installed annode to ptt1-2 (brown side). connected cathode side to c130. rarduino comes on. barely any noise came out of speaker even with antenna connected. then noticed c130 was smoking and melting into board. Does anybody know what capacitor I can switch that with? |
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A junction transistor like the mmbt3904 (the bitx40 schematic is incorrect in labeling them bc849)
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is at first glance symmetrical, running it upside down with emitter and collector reversed could sort of work. But they are optimized for the emitter going to ground, not the collector. Page 2 of the datasheet shows that the base-emitter breakdown voltage is only 6 volts, ? ?? so if the emitter (now pseudo-collector) is at 12v and the base is below 6v that junction will break down like a zener and current will flow. ?Pushing that junction into breakdown can have a permanent effect on gain if current is restricted, and blow the transistor if it isn't. ?Not something they bother to spec though. Assuming the mmbt3904 operating upside down is acting more or less like a normal NPN transistor, with power to the bitx40 reversed the base of Q7 is biased at ? 12v*2.2k/(1k+2.2k) = 8.25v through 1k || 2.2k = 667 ohms and the reversed transistor is in saturation. ?The 470 ohms at R74 is the only thing restricting collector/emitter current flow to around 12v/0.47k=25ma, and Q7 is dissipating 25ma*12v=300mw. ?Would probably survive that, but not by much. Unfortunately, with the pseudo-emitter down near ground, the base will be too despite the best efforts of the biasing resistors at R71 and R72. ?So the pseudo-collector to base voltage will exceed the 6v emitter-base breakdown voltage of the datasheet, and all bets are off. ?? I'm not planning to test my guesses of what might happen on my bitx40 anytime soon. Mine has an LM2940CT-12 regulator in the supply line from the battery. Unlike the older LM7812, the LM2940CT-12 ?will protect against reversed battery leads. It also protects against battery voltages in excess of 12v, and gives some semblance of overcurrent protection. The IRF510 is powered directly from the battery with no protection, ?as the IRF510 is quite cheap. Maybe I'll add a 2A fuse there someday. ?After watching T7, L8, and associated traces fry. Jerry, KE7ER On Mon, Oct 23, 2017 at 08:20 pm, Jerry Gaffke wrote:
Q7 has mostly that 470 ohm emitter resistor to stop excessive reverse current, but probably survived. |
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Vince Vielhaber
tombstone?Yep. Vince.
-- Michigan VHF Corp. |
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I suspect the replacement diode went in the wrong way around, and that was what smoked. Drilling the board to link C130 (and D7) to the relay coil is a bit of overkill: that bit of track goes to a 'via', connecting the two planes, you could have done what I did - use an Xacto knife (I used a box-cutter!) to excise a track-width or so of the ground plane around the via's exit, clean that off as a pad and link it to the nearby coil point. The bit of track on the top having lifted, it could have just been jumpered to the (cleaned-off) top of the via. Oh, well , live and learn ...
73 de ZL2DEX |
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You can put them back if you wish after testing, but "they aren't serving any purpose and can be removed from the board"
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means you don't have to. K1 is one of the two big black boxy things on your board, a relay (which could be called a solenoid switch). The relays are labeled K1 and K2 in the schematic at ? ? Perhaps a bit confusing as each one has two double pole switches plus a coil in the schematic, and while close together they don't have a box around them. ?Each relay has pins into the board labeled in the schematic as??1,3,5,8,9,12,14,16 If you put amps through a part of your DVM that was expecting milliamps, that part of it is probably blown. At least the shunt resistor used for milliamps is blown. ?Could be the damage went further. Test your meter somehow. ?For example, a 12v battery through a 1k resistor will give 12v/1000ohms = 0.012 amps = 12 milliamps and the resistor will have to dissipate 12v*0.012a = 0.144 watts, so a quarter watt resistor should do fine. And 12v/10ohms = 1.2 amps, but that 10 ohm resistor will be dissipating 12*1.2=14.4 watts, so you would want at least a 5 watt resistor for a quick one second test. ?That resistor will get very hot very quickly. On Wed, Oct 25, 2017 at 03:26 am, Barrett O wrote:
Since D7 and C130 ?aren't wired up right, they aren't serving any purpose and can be removed from the boardYou mean remove just temporary for testing?? |
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well I removed d7 and c130 and it doesn't smoke anymore but still not working. I hooked up the antenna. makes weird noise from speaker with no static but what I did notice is if I tune around in different spots it sounds like I can hear jumbled voices.
I will probably end up ordering another board and tackle this again later on when I feel more advance or there is a guy at the local ham club that has a lot of experience with electronics. Maybe I will ask him if he wants to look at it with me |
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Well my new kit came in and you wont believe this it turns out my audio jack had went bad. I put the old board back in and it receives just fine and also transmits but the transmit power is very low. the needle moves maybe an 8th of where it did.
Do yall have any ideas on what could be causing the out put to be low because other than that it seems to work? -- Barrett K5SSO |
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